Expression of α-subunit and luteinizing hormone (LH) β messenger ribonucleic acid in the rat during lactation and after pup removal: Relationship to pituitary gonadotropin-releasing hormone receptors and pulsatile LH secretion

L. R. Lee, D. J. Haisenleder, J. C. Marshall, M (Susan) Smith

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

Pituitary GnRH receptor (GnRH-R) levels and LH secretion are suppressed in the lactating rat. To determine if LH synthesis is also inhibited, we have measured LH subunit mRNA levels in the pituitary of lactating rats. We have also examined the temporal relationship among restoration of GnRH-R, LH secretion, and LH synthesis after withdrawing the sensory stimulus of suckling. Pituitary α-subunit and LHβ mRNA levels were sharply reduced on day 10 of lactation in both intact and ovariectomized (OVX) animals compared with those in cycling diestrous rats or OVX controls. Removal of the suckling stimulus from OVX animals led to significant increases in α-subunit and LHβ mRNA levels by 24 h. Upon removal of the suckling stimulus from intact rats, α-subunit mRNA levels were restored by 48 h, but LHβ mRNA levels did not return to diestrous levels until 72 h. Pituitary GnRH-R levels were clearly up-regulated within 1 day after pup removal. Some LH pulses were observed by 48 h, but consistent plasma LH pulses were not detected until 72 h. When pulsatile GnRH was administered during the 24 h after pup removal from intact rats, the regimen of pulsatile GnRH was successful in inducing LH secretion; however, the restoration of pulsatile LH was not accompanied by increases in α-subunit and LHβ mRNA levels. The present studies provide further evidence to support the hypothesis that during lactation, the suppression of pituitary gonadotroph function is mainly due to the loss of hypothalamic GnRH secretion. Our data also show that 1) the restoration of GnRH-R alone is not sufficient to activate LH subunit mRNA and LH secretion; 2) the normal restoration of pulsatile LH secretion and increases in LH subunit mRNA are temporally correlated, as increases in LH secretion appear to precede increases in LH subunit mRNA; and 3) the restoration of pituitary LH subunit mRNA levels and pulsatile LH secretion took longer in the intact rat than in the OVX rat, suggesting that ovarian steroids may play a role in the inhibitory effect of lactation.

Original languageEnglish (US)
Pages (from-to)776-782
Number of pages7
JournalEndocrinology
Volume124
Issue number2
StatePublished - 1989
Externally publishedYes

Fingerprint

LHRH Receptors
Pituitary Gonadotropins
Pituitary Hormones
Luteinizing Hormone
Lactation
RNA
Messenger RNA
Gonadotropin-Releasing Hormone

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

Cite this

Expression of α-subunit and luteinizing hormone (LH) β messenger ribonucleic acid in the rat during lactation and after pup removal : Relationship to pituitary gonadotropin-releasing hormone receptors and pulsatile LH secretion. / Lee, L. R.; Haisenleder, D. J.; Marshall, J. C.; Smith, M (Susan).

In: Endocrinology, Vol. 124, No. 2, 1989, p. 776-782.

Research output: Contribution to journalArticle

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abstract = "Pituitary GnRH receptor (GnRH-R) levels and LH secretion are suppressed in the lactating rat. To determine if LH synthesis is also inhibited, we have measured LH subunit mRNA levels in the pituitary of lactating rats. We have also examined the temporal relationship among restoration of GnRH-R, LH secretion, and LH synthesis after withdrawing the sensory stimulus of suckling. Pituitary α-subunit and LHβ mRNA levels were sharply reduced on day 10 of lactation in both intact and ovariectomized (OVX) animals compared with those in cycling diestrous rats or OVX controls. Removal of the suckling stimulus from OVX animals led to significant increases in α-subunit and LHβ mRNA levels by 24 h. Upon removal of the suckling stimulus from intact rats, α-subunit mRNA levels were restored by 48 h, but LHβ mRNA levels did not return to diestrous levels until 72 h. Pituitary GnRH-R levels were clearly up-regulated within 1 day after pup removal. Some LH pulses were observed by 48 h, but consistent plasma LH pulses were not detected until 72 h. When pulsatile GnRH was administered during the 24 h after pup removal from intact rats, the regimen of pulsatile GnRH was successful in inducing LH secretion; however, the restoration of pulsatile LH was not accompanied by increases in α-subunit and LHβ mRNA levels. The present studies provide further evidence to support the hypothesis that during lactation, the suppression of pituitary gonadotroph function is mainly due to the loss of hypothalamic GnRH secretion. Our data also show that 1) the restoration of GnRH-R alone is not sufficient to activate LH subunit mRNA and LH secretion; 2) the normal restoration of pulsatile LH secretion and increases in LH subunit mRNA are temporally correlated, as increases in LH secretion appear to precede increases in LH subunit mRNA; and 3) the restoration of pituitary LH subunit mRNA levels and pulsatile LH secretion took longer in the intact rat than in the OVX rat, suggesting that ovarian steroids may play a role in the inhibitory effect of lactation.",
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